[gnome-software] appstream: Fix plugin failing to load if applications directory doesn't exist

[Richard Hughes <rhughes src gnome org>]

commit 52f1fa25a8150ea8f69c627c21e873a8b0cbb9bd
Author: Robert Ancell <robert ancell canonical com>
Date:   Fri Mar 20 17:05:17 2020 +1300

    appstream: Fix plugin failing to load if applications directory doesn't exist
    
    Due to an ordering bug gs_plugin_appstream_load_desktop() can set a GError and return TRUE.
    This causes the appstream plugin to hit an assertion and fail to start:
    XbSilo xb_builder_ensure: assertion 'error == NULL || *error == NULL' failed

 plugins/core/gs-plugin-appstream.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)
---
diff --git a/plugins/core/gs-plugin-appstream.c b/plugins/core/gs-plugin-appstream.c
index 4d8ba517..037653c1 100644
--- a/plugins/core/gs-plugin-appstream.c
+++ b/plugins/core/gs-plugin-appstream.c
@@ -264,12 +264,17 @@ gs_plugin_appstream_load_desktop (GsPlugin *plugin,
                                  GError **error)
 {
        const gchar *fn;
-       g_autoptr(GDir) dir = g_dir_open (path, 0, error);
-       g_autoptr(GFile) parent = g_file_new_for_path (path);
-       if (!g_file_query_exists (parent, cancellable))
-               return TRUE;
+       g_autoptr(GDir) dir = NULL;
+       g_autoptr(GFile) parent = NULL;
+
+       dir = g_dir_open (path, 0, error);
        if (dir == NULL)
                return FALSE;
+
+       parent = g_file_new_for_path (path);
+       if (!g_file_query_exists (parent, cancellable))
+               return TRUE;
+
        while ((fn = g_dir_read_name (dir)) != NULL) {
                if (g_str_has_suffix (fn, ".desktop")) {
                        g_autofree gchar *filename = g_build_filename (path, fn, NULL);